Preliminary Design Of Fiber Pulsed Coherent Wind Lidar

All-fiber Coherent Doppler Wind Lidar(CDL) is developed based on coherentfiber communication. Fiber is used to connect components of the Lidar system. SoAll-fiber CDL has advantage in system stability, portability and long service lifewhich make it easy-to-business. With optical heterodyne detecting Doppler frequencyshift of aerosol, it is easy to realize a velocity resolution less than1m/s in wind fieldsounding.The paper analyzes the effect of atmosphere turbulence and aerosol distributionon coherent detection. First, the causes and characteristics of the atmosphere areanalyzed, which explaining why it influences the propagation of laser. Based on therelationship between turbulence and CDL wind sounding, the paper explains how tooptimize the detection performance by system design.The key of CDL is coherence of local oscillation light and the backscatter lightfrom atmosphere. The paper discusses the effect on heterodyne detecting frompropagation angle and angle of polarization direction between LO light andbackscatter light, which provide a reference for designing system. In addition, thecarrier-to-noise ratio is a parameter that reflecting the capability of coherent detection.The influences of the LO shot noise, detector noise, LO relative intensity noise andleak pulse of acoustic-optical modulator on coherent detection are discussed and therelation between CNR and velocity resolution is analyzed in the paper.The coupling of free space light into tiny fiber is a difficulty lies in All-fiber CDL.A optimum optical antenna is important to the system. The paper analyzed therelationship between optical antenna aperture and backscatter signal receiving basedon CDL equation and turbulence theory.Finally, the paper discusses the radial velocity inversion method. With Matlabcode and Fast Fourier Transformation transforms time domain signal to frequencydomain signal where the Doppler frequency shift is abstracted and correspondingvelocity calculated to inverse wind field. In case of the absence of pulse fiber laserordered, the data processing method for All-fiber pulse CDL wind velocity is testedon a simulated pulse CDL signal and get the velocity profile of wind. Further, thevapor flow from a humidifier is detected by a continuous wave fiber CDL which usethe same optical antenna and approximate data processing method, refer to thefeasibility of optical design and data processing in certain degree.